The High Voltage Electron Microscope Laboratory at the University of Wisconsin began operation as a national facility in the spring of 1972 supported by a grant from the Biotechnology Resources Program of the Research Resources Division of NIH. The present proposal requests funds the operation of this national facility during the next five years. The main purpose of this facility is to make available to qualified biomedical researchers a Million Volt Electron Microscope. The high voltage electron microscope allows imaging of thick specimens such as whole mounts of cells or organelles and sections up to several microns thick with reasonable resolution (about 2 nm with al microns tissue section). The staff of the facility maintains the equipment, advises and aids in the use of it and is involved in continuous improvement and broadening of applications of HVEM in biomedical research. This includes developing methods of specimen preparation, of stereoscopic recording, of studying hydrated specimens and high resolution studies of crystalline arrays of biological macromolecules.